The invention relates to the protection of ATM connections in a network which includes at least one protection domain which covers only a portion of a connection. Each protection domain comprises a first access node and a second access node. Each of these access nodes can switch over from a first connection to a second connection in the event of the first connection failing. For the direction of transmission going from the first access node to the second access node, the first access node is called the xe2x80x9csourcexe2x80x9d node, and the second access node is called the xe2x80x9csinkxe2x80x9d node.
Until now, the existing protection method has been applicable only when the protection domain covers a complete connection from end to end. It is based on the Alarm Indicator Signal (AIS) function: AIS cells are sent downstream to inform downstream nodes about a transmission fault. It uses an xe2x80x9cAutomatic Protection Switchingxe2x80x9d (APS) protocol. When a sink node receives an AIS cell; it sends a switchover request message to the source node by means of an APS cell. Then the source node and the sink node both switch over.
When a protection domain covers only a portion of a connection, that method is not applicable because the sink node cannot tell whether the AIS cell originates from a node located before or after the source node.
The aim of the invention is to propose a method which is applicable when the network includes at least one protection domain covering only a portion of a connection, without changing anything in the present definition of the AIS function, for simplicity and for backward compatibility with the present state of the art. In the invention, protecting the ATM connection is a separate problem from Operation And Maintenance (OAM), and therefore it can be solved separately. Since APS cells have been created specifically for this problem, the proposed method is based on using such APS cells, and AIS cells are used for triggering the APS mechanism.
The invention provides a method of protecting ATM connections in a telecommunications network including at least one protection domain which covers only a portion of a connection, each protection domain comprising a source node and a peer sink node, each source node and its peer sink node being capable of being interconnected by at least two alternative connection segments and being capable of switching over from one connection segment to the other; any node of the network being capable of detecting a connection fault upstream and of sending an alarm message downstream via the current path, and each node being capable of storing a fault connection status when it receives such an alarm message; the method comprising the following steps:
in each sink node which receives the alarm message, sending a switchover request message to its peer source node to request a switchover, which request is executed only if the peer source node has not itself stored an alarm message;
and then, in said sink node, switching over only if the peer source node has responded positively.
Preferably, the invention further consists in sending a confirmation message from a sink node to a peer source node in order to confirm that the sink node is switching over, and in switching over in the source node only if the source node receives the confirmation message.